1. Field of the Invention
The present invention relates to an image detection and readout apparatus that includes a solid state detector constructed to record an image as an electrostatic latent image, and to generate electrical currents according to the electrostatic latent image when scanned by readout light, a surface light source constituted by multitudes of linear light sources arranged in parallel, each for emitting readout light, and a light source control means configured to sequentially switch and drive the linear light sources to cause the scanning to be performed by the linear light sources.
2. Description of the Related Art
Today, various types of radiation image recording/readout systems that use a solid state radiation detector (hereinafter also referred to as simply “detector”) are proposed in the field of radiation imaging for medical diagnosis and the like. The solid state radiation detector described above temporarily stores electric charges in the charge storage section as latent image charges obtained by detecting radiation and outputs electrical signals representing the radiation image information by converting the latent image charges. Various types of detectors are proposed as the solid state radiation detector for use in such systems. From the aspect of charge reading out process in which charges stored in the detector are read out, some of the detectors are categorized into the optical readout type in which the charges are read out by irradiating readout light (readout electromagnetic wave) on the detector.
The inventor of the present invention has proposed a detector having a fast readout response along with an efficient signal charge readout capability as one of the optical readout type solid state radiation detector as described in U.S. Pat. Nos. 6,268,614 and 6,770,901. The detector has a set of layers layered in the order of: a first conductive layer having transparency to recording radiation or light excited by the recording radiation (hereinafter referred to as “recording light”); a recording photoconductive layer that shows conductivity when exposed to the recording light; a charge transport layer that acts as substantially an insulator against charges of the same polarity as the charges charged on the first conductive layer and as substantially a conductor for the charges of the opposite polarity; a readout photoconductive layer that shows conductivity when exposed to readout light; a second conductive layer having transparency to the readout light. The layer composite has a charge storage section formed between the recording photoconductive layer and charge transport layer for storing latent image charges (electrostatic latent image) representing image information.
In particular, the solid state radiation detector proposed by the inventor of the present invention as described in U.S. Pat. No. 6,770,901 uses a stripe electrode constituted by multitudes of charge detecting linear electrodes having transparency to readout light as the electrode of the second conductive layer having transparency to readout light. In addition, multitudes of auxiliary electrodes for outputting electrical signals corresponding to the amount of latent image charges stored in the charge storage section are provided in the second conductive layer alternately and in parallel with the charge detecting linear electrodes.
By providing the sub-stripe electrode constituted by the multitudes of auxiliary linear electrodes in the second conductive layer, a capacitor is newly formed between the charge storage section and the sub-stripe electrode. This allows the transport charges of the opposite polarity to that of the latent image charges stored in the charge storage section by the recording light to be charged also on the sub-stripe electrode by the rearrangement of charges in the charge reading out process. This may reduce the amount of transport charges to be allocated to the capacitor formed between the stripe electrode and charge storage section with the readout photoconductive layer being sandwiched between them to relatively small compared with the case where no such sub-stripe electrode is provided. Consequently, the amount of signal charges which may be read out from the detector to outside is increased and the readout efficiency is improved, resulting in a fast readout response with an efficient signal charge extraction capability.
Further, an image detection and readout system that includes a solid state detector of the type described above, a surface light source constituted by multitudes of linear light sources arranged in parallel, each for emitting readout light, and a light source control means configured to sequentially switch and drive the linear light sources to cause the scanning to be performed by the linear light sources is proposed as described, for example, in U.S. Pat. No. 6,376,857.
In the mean time, an electrode of several tens of centimeters long with several tens of micrometers wide is envisages to be used as the linear electrodes constituting the stripe electrode of the solid state detector described above. The stripe electrode constituted by such long and narrow linear electrodes has a large resistance component which degrade S/N ratio of the image signals read out from the solid state detector. Further, such stripe electrode has a large capacitance component due to the spacing as narrow as several tens of micrometers between the adjacent linear electrodes. This also degrades S/N ratio of the image signals read out from the solid state detector.
In the embodiment disclosed in the U.S. Pat. No. 6,376,857, when obtaining image signals from such solid state detector, the image signals are obtained from the solid state detector by sequentially driving a plurality of linear light sources extending in the direction orthogonal to the length direction of the linear electrodes and scanning the solid state detector by the readout light emitted from each of the linear light sources. As described above, each of the linear electrodes is as long as several tens of centimeters. This brings about a problem that it takes a long time to scan over the entire length of the linear electrodes by sequentially driving the linear light sources.
The present invention has been developed in view of the circumstances described above. It is an object of the present invention to provide an image detection and readout apparatus capable of improving S/N ratio of detected signals and enhancing image signal acquisition speed. The apparatus includes a solid state detector constructed to record an image as an electrostatic latent image, and to generate electrical currents according to the electrostatic latent image when scanned by readout light; a surface light source constituted by multitudes of linear light sources arranged in parallel, each for emitting readout light; and a light source control means configured to sequentially switch and drive the linear light sources to cause the scanning to be performed by the linear light sources.